Oral compositions for ruminants

Description

[0001] The present invention relates to oral compositions for ruminants and more specifically relates to delayed-­release coating agents for the preparation of supplements to feedstuffs for ruminants which comprise a core of at least one physiologically active substance. The present invention also relates to supplements to ruminant feedstuffs formulated with such coating agents.

[0002] It is known that the pH in the first stomach of a ruminant is about 5.5 and that various microorganisms exhibit fermentation activity in the first stomach where feedstuffs are retained for about 6 to 30 hours. In cases where veterinarially acceptable, physiologically active substances (hereinafter referred to as active substances) such as, amino acids, are given per os to ruminants such as cattle and sheep, effective absorption of the active substances in the fourth stomach (having a pH of about 3) and succeeding digestive tract is much reduced because they have been degraded while in the first stomach [as disclosed in US Patent 4196187].

[0003] In order to avoid this problem, various proposals have hitherto been made to protect the active substances. For example, the provision of a core of active substance covered with a coating agent which is capable of inhibiting the decomposition of the active substances in the first stomach, and which does no inhibit absorption in the fourth stomach and succeeding digestive tract have been suggested.

[0004] Examples of such proposals include the use of a capsule prepared by using a coating agent comprising triglycerides, such as hydrogenated fats originating from plants and animals, waxes and mixtures thereof [as disclosed in Japanese Patent Application-A-12785/73]. An additive to feedstuffs formulated into a pellet containing an active substance in admixture with an excipient (such as magnesium oxide, magnesium carbonate, calcium carbonate, and aluminium hydroxide) and coated with a coating agent comprising a polymer (for example a copolymer of cellulose propionate, morpholinobutylate or dialkylaminoethyl acrylate with methacrylate) is disclosed in Japanese Patent Application-A-46824/79. An additive to feedstuffs containing an active substance and coated with a coating agent comprising a high molecular compound (for example, cellulose propionate morpholinolactate, a copolymer of vinylpyridine with styrene or a copolymer of 2-methyl-5-vinylpyridine with styrene or acrylonitrile and a hydrophobic substance (for example, oleic acid, stearic acid and palmitic acid) is disclosed in Japanese Patent Application-A-46825/79. An additive to feedstuffs has been prepared by using a coating agent comprising chitosan and at least one member selected from saturated or unsaturated monocarboxylic acids having 14-22 carbon atoms and hardened animal fats, as disclosed in US Patent 4533557. A coating agent comprising ethylcellulose and a synthetic high molecular compound which is soluble in water at a pH of not higher than 5 is disclosed in Japanese Patent Application-A-88843/86. An additive to feedstuffs has been prepared by using a coating agent which comprises a first component, viz. a synthetic high molecular compound which is soluble in water at a pH of not higher than 5 and a second component viz. at least one member selected from fats, waxes, saturated or unsaturated aliphatic alcohols having 14-32 carbon atoms and saturated or unsaturated fatty acids having 14-37 carbon atoms [as disclosed in Japanese Patent Application-A-88844/86].

[0005] The provision of an improved coating agent is however still required because known coating agents have, in general, either the disadvantage that if it is capable of exerting higher protection in the first stomach then it is only decomposed slowly in the fourth stomach, or it is decomposed rapidly in the fourth stomach but is liable to exert insufficient protection in the first stomach.

[0006] The present invention is based upon the discovery that the protecting acitivity of coating agent disclosed in Japanese Patent Application-A-88843/86 may be improved unexpectedly by addition of a certain substance which is solid at room temperature, soluble in organic solvents water and insoluble in water.

[0007] According to one aspect of the present invention, there is provided a coating agent for delaying the release of a physiologically active substance to be administered per os to ruminants, comprising a veterinarially acceptable water-soluble, synthetic high molecular compound and ethylcellulose, said coating agent being stable in the first stomach of ruminants and capable of being effectively disintegrated in the fourth stomach of ruminants, characterized in that said coating agent furher comprises at least one substance which is miscible with both of said high molecular weight compound and ethylcellulose and is insoluble in water.

[0008] According to another aspect of the present, there is provided a delayed-release veterinary composition for oral administration to ruminants, comprising one or more physiologically active substances coated with an effective amount of a coating agent of the first aspect of the invention.

[0009] For the purpose of the present invention, various veterinarially acceptable, physiologically active substances of known type may be used. Examples include amino acids such as methionine, lysine, tryptophan, threonine, glutamic acid, glutamine and asparagine; amino acid derivatives or peptides thereof such as dopa-glutathione; vitamins such as vitamin A; enzymes such as acid protease; sugars such as glucose; anti­biotics such as penicillin; and anthelmintics such as levamisole. These active substances may be used alone or in combination.

[0010] The coating agent according to the present invention may be used with advantage for the preparation of feedstuff supplements for various ruminants such as, for example, cattle, sheep and goats.

[0011] Veterinarially acceptable, high molecular compounds which may be used in coating agents according to the present invention include various known compounds which are wet-proof and soluble in water at a pH of not more than 5. Preferred high molecular compounds are exemplified as follows:-

(1) Polyvinyl acetal diethylaminoacetate. Advantageously those having a molecular weight of from 30,000 to 150,000 and containing 1.0-5.5% (w/w) of nitrogen such as, for example, AEA (commercially available from Sankyo K.K. Japan) may be used.

(2) Copolymers formed with dimethylaminoethyl meth­acrylate and at least one member selected from alkyl esters of methacrylic acid and alkyl esters of acrylic acid. Advantageously those having a molecular weight of from 50,000 to 500,000 and containing 3-8% (w/w) of nitrogen such as, for example, Eudragit A E100 (solid), E12.5 (12.5% suspension) (copolymers of dimethylaminoethyl methacrylate, methylmethyacrylate and butylmethacrylate; commercially available from Rhom Pharma, West Germany) may be used.

(3) Copolymers formed with 2-methyl-5-vinylpyridine and at least one member selected from alkyl esters of methacrylic acid and alkyl esters of acrylic acid, methacrylic acid and acrylic acid. Advantageously those having a molecular weight of from 5,000 to 400,000 and containing 2-15% (w/w) of nitrogen such as, for example, MPM-47 (commercial product of Tanabe Seiyaku K.K., Japan; copolymer formed with 2-methyl-­5-vinylpyridine, methacrylate and acrylic acid) may be used.

[0012] With regard to the above-mentioned monomers, preferred alkyl groups of alkyl esters are exemplified by straight of branched alkyl groups having 1-8 carbon atoms such as ethyl, i-propyl n-butyl and 2-ethylhexyl groups.

[0013] It is preferred to use ethylcellulose containing 2.0-2.8% (w/w) of ethoxy groups per one unit of glucose.

[0014] In order to achieve disintegration of the coating agent in the fourth stomach with good results, various water-insoluble substances which are miscible with both of the above-mentioned high molecular weight compound and ethylcellulose may be used.

[0015] It is advantagerous to use a water-insoluble substance which is solid at room temperature to aid manufacture.

[0016] Moreover, with regard to formation of a stronger coating layer, it is advantageous to use those which are soluble in various solvents such as, for example, isopropanol, ethanol, dichloromethane, acetone, ethyl acetate and ethylene glycol monoethyl ether. Substances which may be used include, for example, saturated fatty acids having more than 14 carbon atoms, higher aliphatic alcohols having more than 12 carbon atoms, hardened oils of plant or animal origin, natural resins and synthetic resins.

[0017] Preferred examples of saturated fatty acids having more than 14 carbon atoms include myristic acid, stearic acid and palmitic acid.

[0018] Preferred examples of higher aliphatic alcohols having more than 12 carbon atoms include lauryl alcohol, myristyl alcohol, cetyl alcohol and stearyl alcohol.

[0019] Preferred examples of animal and plant oils include hardened oil orginating from beef tallow and hardened caster oil.

[0020] Preferred examples of natural resins and synthetic resins include shellac and vinyl acetate.

[0021] The weight ratio of the high molecular compound to ethylcellulose contained in the coating agent of the present invention may be, for example, from 1:0.5 to 1:10 (preferably from 1:1 to 1:7).

[0022] We have found that, in the case where the ratio of ethylcellulose is smaller than 1:0.5, a large amount of the active substances such as, for example, amino acids may be dissolved in the first stomach, and thereby become available to microorgnaisms for decomposition while in the other case where the ratio is greater than 1:10, the active substances may not be sufficiently available in the fourth stomach and succeeding digestive tract.

[0023] The weight ratio of the water-insoluble substance to ethylcellulose may be, for example, from 1:0.1 to 1:20 (preferably from 1:0.5 to 1:2).

[0024] Advantageously, the coating agent may be in solid form and may, if desired, contain various known plasticizers such as, for example, polethylene glycol, triacetin and Myvacet (commercial product of Eastman Kodak Corpn., U.S.A.); anti-coagulating agents such as, for example, talc and magnesium stearate. The amount of such additives in total is preferably not more than 30% (w/w).

[0025] The ratio of the above-mentioned high molecular compound to the water-insoluble substances present in the coating agent is preferably more than 50% (for example, more than 1:0.7) be weight.

[0026] Usually, the core may be solid and may, if desired, contain various known binders such as, for example, hydroxypropyl cellulose, polyvinyl pyrrolidone and polyvinyl alcohol; excipients such as, for example, lactose, mannitol and crystalline cellulose: and disintegrants such as, for example, potato starch, corn starch, carboxymethyl cellulose calcium carboxy­ methyl cellulose sodium and crystalline cellulose.

[0027] The ratio of the coating agent to the active substances coated thereby exerts a significant influence upon the availability and value of the active substances. Thus, for example, it is advantageous to use the coating agent at a weight ratio of 5-100 parts per 100 parts of the core. We have found that, in the case where the amount of the coating agent is insufficient (for exmaple, not more than 5), the active substances are excessively decomposed or disintegrated in the first stomach, while in the case where the ratio of the coating agent is excessively high (for example, more than 100 parts), there is insufficient absorption of the active substances in the fourth stomach and succeeding digestive tract.

[0028] An oral composition according to the present invention may be obtained by drying a granule containing at least one active substance and coating the dried granule with a coating agent according to the present invention. The granule may be prepared by adding a suitable binder dissolved in a suitable solvent to at least one active substance and kneading the mixture to obtain the desired granule. The concentration of solids present in the binder solution is, for example, 3-20% w/w.

[0029] Granules may be prepared in conventional manner by using for example a cylindrical or spherical granulator. Alternatively, it is also possible to prepare granules in the form of crystals or spheres and then coat them with an agent according to the invention.

[0030] In the case where at least two active substances are used, it is advantageous to prepare a granule by applying a binder solution onto a core containing a first active substance having a higher solubility in the solvent (e.g. water) to be used for the preparation of the binder solution, and then applying a second active substance having a lower solubility in the solvent onto the core, for example, by spray-drying thereby to obtain the desired granule. Thus, for example, in order to obtain granules containing lysine and methionine, cores are prepared by treating crystalline lysine or granulated lysine by means of a centrifuge-­fluidizing granulating machine (for example, CF-granulator, CF-360, commercial product of Freund Sangyo K.K., Japan). Powdered methionine and an aqueous binder solution are then fed to the granules containing lysine. The diameter of the core containing the active substance having a higher solubility is, for example, about 0.5-3.0 mm. The resultant granules are then dried using, for example, hot air at a suitable temperature for a suitable period of time (for example, at a temperature of 30-70°C for 30-90 minutes) to obtain dried granules having a diameter of, for example, about 1.4-3.2 mm. The dried granules may then be coated, for example, by spray-coating a coating solution having a suitable concentration of solids, for example, 1-10% w/w. It is possible to add to the solution excipients, disintegrants and/or binders, which may be dissolved, if desired, in a suitable solvent such as, for example, water or ethanol before use.

[0031] Examples of the solvents which may be used for the preparation of the coating agent of the present invention include those capable of dissolving the water soluble high molecular compound of the present invention such as dichloromethane, ethanol, isopropanol, acetone and ethyl acetate, which may be used alone or in combination.

[0032] In order to improve absorption of the active substances it is advantageous to effect dissolution of the active substances at a higher rate in the fourth stomach. However, use of a coating agent not containing a water-insoluble substance, leads to the disadvantage that the ethylcellulose layer is not disintegrated, even when the synthetic high molecular substance has already been dissolved (owing to the solubility of the high molecular compound at the pH in the fourth stomach). Moreover, the strength of the coating agent is liable to decrease rapidly after the dissolution of the high molecualr weight compound if an excessively large amount of the water-soluble substance is used.

[0033] It is preferred that a coating agent according to the present invention is wet-proof at a generally neutral pH and may be disintegrated at a lower pH e.g. below 5. Disintegration of the coating agent which is for example, in the form of a thin layer on the surface of the granule, may begin at a relatively low pH because of the use of a water-insoluble substance which is miscible with both the synthetic high molecular compound and ethylcellulose. As a result, the active substances are protected in the first stomach but dissolved effectively in the fourth stomach and succeeding digestive tract.

[0034] It is possible to make the coating agent effectively wet-proof and also to limit the amount of the coating agent used and thus improve the value of the coating agent.

[0035] The following non-limiting examples and experiments illustrate the present invention.

Example 1

[0036] 400 g of an aqueous solution of polyvinyl alcohol (20% w/w) was added to DL-methionine (2000 g) as a binder. The mixture was well kneaded and then treated using a cylindrical granulating device equipped with a screen to give granules having a diameter of 2.0 mm. The granules were made spherical by using a Marumerizer (a machine, produced by Fuji-Paudaru K.K., Japan) and were then graded by using a sieve of 10-12 mesh. the granules were air-dried at a temperature of 60°C for one hour to obtain dried granules having a diameter of 1.4-1.8 mm.

[0037] Separately, a mixture of ehtylcellulose (150 g), stearic acid and AEA (4:2:3 w/w) and Myvacet distilled acetylated monoglyceride Type 9-40 (30g) were dissolved in a mixture of isopropanol and acetone (3000 g 2:1 v/v). Magnesium stearate (25 g; anti-coagulating agent) was added thereto to prepare a coating solution. A fluidizing bed was used to apply the coating solution to the above-mentioned granules (1000 g) by spray-­coating. The coating agent (10 parts per 100 parts of granules on solid basis) was coated onto the granules to obtain granules containing 90% w/w of methionine.

Example 2

[0038] Ethylcellulose, polyvinyl acetate and AEA (3:3:3 w/w; 150 g in total) and Myvacet Type 9-40 (30g) were dissolved in a mixture of ethanol and acetone (3000 g 3:1 v/v). Magnesium stearate (25 g; anti-coagulating agent) was added thereto to prepare a coating solution. In a similar manner to that described in Example 1, a coating solution (10 parts by weight) containing solids was applied by spray-coating onto 100 parts by weight of the granules (diameter: 1.7-2.4 mm). There were obtained coated granules having a slightly increased diameter and containing 90% w/w of methionine.

Comparative test 1

[0039] A mixture of ethylcellulose and AEA (150 g; 6:3 w/w) and Myvacet Type 9-40 (30g) were dissolved in a mixture of ethanol and acetone (3000 g; 3:1 v/v). Magnesium stearate (25 g; anti-coagulating agent) was added thereto to prepare a coating solution. In a similar manner to that described in Example 1, the resultant coating solution (10 parts by weight) containing solids was applid onto the granules having a diameter of 1.7-2.4 mm (100 parts by weight) by spray-coating. There were obtained granules containing methionine (90% w/w) and covered with a coating agent lacking a synthetic high molecular compound.

Example 3

[0040] 2000 g of lysine hydrochloride was added to 700 g of an aqueous ethanol (ethanol: water=1:1 v/v) containing hydroxypropyl cellulose (6% w/w) as a binder. The mixture was well kneaded and transferred to a cylindrical granulating device equipped with a screen to give granules having a diameter of 2.0 mm, which were then made spherical by using a Marumerizer and were then graded by using a sieve of 8-10 mesh. The granules were air-dried at a temperature of 50°C for one hour to obtain dried granules having a diameter of 1.7-2.4 mm.

[0041] Separately, a mixture of ethylcellulose, stearic acid and Eudragit E100 (150 g: 3:2:1 w/w) and Myvacet Type 9-40 (30 g) were dissolved in a mixture of ethanol and acetone (3000 g; 2:1 v/v). Magnesium stearate (25 g; anti-coagulating agent) was added thereto to prepare a coating solution. A fluidizing bed was used to apply the coating solution to the above-­mentioned granules by spray-coating. The coating solution (10 parts per 100 parts of granules on solid basis) was coated onto the granules to obtain granules containing 90% w/w lysine protected by a coating agent according to the invention.

Comparative test 2

[0042] A mixture of ethylcellulose and Eudragit E100 (150 g; 5:1 w/w) was dissolved in a mixture of ethanol and acetone (3000 g; 3:1 v/v). Magnesium stearate (25 g; anti-coagulating agent) was added thereto to prepare a coating solution. In a similar manner to that described in Example 3, the coating solution (10 parts by weight) containing solids was applid onto the granules having a diameter of 1.7-2.4 mm (100 parts by weight) by spray-coating. Granules containing methionine (90% w/w) covered with a coating agent lacking a miscible substance were obtained.

Example 4

[0043] A binder solution (700 g) was prepared by adding hydroxypropyl cellulose (6% w/w) to an aqueous ethanol (ethanol: water=1:1 v/v) which was then mixed with lysine hydrochloride (2000 g). The mixture was well kneaded and treated by using a cylindrical granulating device equipped with a screen to give granules having a diameter of 2.0 mm. The granules were made spherical by using a Marumerizer and were then graded using a sieve of 8-10 mesh. The granules were air-dried at a temperature of 60°C for one hour to obtain dried granules having a diameter of 1.7-2.4 mm.

[0044] Separately, a mixture of ethylcellulose, vinyl acetate and AEA (150 g: 5:1:3 w/w) were dissolved in a mixture of dichloromethane and ethanol (300 g; 3:3 v/v) to prepare a coating solution. The solution (10 parts per 100 parts of granules on solid basis) was applied onto the granules by spray-drying to obtain coated granules containing 90% w/w of methionine.

Comparative test 3

[0045] A mixture of ethylcellulose and AEA (150 g; 6:3 w/w) was dissolved in a mixture of dichloroethane and ethanol (3000 g; 1:1 v/v) to prepare a coating solution. In a similar manner to that described in Example 4 the coating solution (10 parts per 100 parts of granules by weight on solid basis) was coated onto the granules to obtain granules containing lysine (90% w/w) covered with a coating agent lacking a synthetic high molecular compound.

Example 5

[0046] Crystals of lysine (1500 g) having a diameter of 1.5-2.0 mm were put into CF-granulator and then powdered methionine (1500 g) and a solution of polyvinyl alcohol (90g) and water (510 g) were added to prepare coated granules. The resultant granules were air-­dried at a temperature of 60°C for one hour to obtain dried granules having a diameter of 1.5-3.0 mm. A fluidizing bed was used to apply to the granules a coating solution prepared in a similar manner to that described in Example 2 to obtain granules coated with the coating agent (10 parts per 100 parts of granules on solid basis); each granule containing 44% w/w of lysine and 44% w/w of methionine.

Comparative test 4

[0047] A binder solution was prepared by dissolving polyvinyl alcohol (90 g) in water (450 g). The binder solution was combined with a mixture of powdered methionine and lysine (each 1500 g). The mixture was well kneaded for 10 minutes using a ribbon-type kneader. The material was then treated by using a cylindrical granulator equipped with a screen to give granules having a diameter of 2.0 mm which were made spherical by using a Marumerizer. The granules were air-dried at a temperature of 60°C for one hour to obtain dried granules having a diameter of 1.5-3.0 mm. A fluidizing bed was used to apply the coating solution described in Example 2 (10 parts per 100 parts of granules on solid basis). Granules, each containing 44% w/w of lysine and of methionine.

Experiment 1

[0048] The granules containing methionine and/or lysine was prepared as described in Examples 1 to 5 and comparative tests 1-4. They were used to carry out a dissolution test at pH 3.0 or 6.0 (which correspond to the pH in the fourth and first stomachs respectively) in the following manner:-
(1) Test conditions:-

Test solutions	- pH 3.0 potassium (I) citrate/hydrochloric acid
	- pH 6.0 potassium (I) citrate/NaOH
Volume	- 500 ml
Temperature	- 37°C
Sample	- 500 mg
Determination	-
Methionine	- HPLC method using a column packed with silica gel (Nucleosil C18; commercial product of Nihon Gasukuro K.K., Japan), and determined at 210 nm.
Lysine	- Ninhydrin reaction, Optical Density at 565 nm.
Test method	- Dissolution test by the paddle method (100 r.p.m.) with reference to The General Method No. 46, Pharmacopoeia of Japan, 11th Edition

(2) The results are shown in the following Tables 1-3. where EX and CT respectively denote the Examples and comparative tests described above.

TABLE 1

Time (hour)	Dissolution ratio (%)
	EX 1		EX 2		CT 1
	pH 6.0	3.0	6.0	3.0	6.0	3.0
0.25	0	98.7	0	72.6	0	5.1
0.5	0	100	0	98.5	0	10.7
1.0	0	100	0	100	0	53.0
2.0	0	100	0	100	0	79.4
3.0	0	100	0	100	0	84.1
4.0	0	100	0	100	0	90.1
5.0	0	100	0	100	4.5	96.4

TABLE 2

Time (hour)	Dissolution ratio (%)
	EX 3		CT 2		EX 4		CT 3
	pH 6.0	3.0	6.0	3.0	6.0	3.0	6.0	3.0
0.5	0	80.5	0	12.7	0	95.7	0	22.6
1.0	0	91.9	0	58.3	0	100	0	71.3
2.0	0	98.7	0	81.6	0	100	0	84.5
3.0	0	100	7.1	90.1	0	100	3.9	97.8
4.0	0	100	15.3	98.8	0	100	10.1	100
5.0	0	100	26.1	100	0	100	20.6	100

TABLE 3

Time (hour)	Dissolution ratio (%)
	EX 5				CT 4
	6.0		3.0		6.0		3.0
	Ly	Me	Ly	Me	Ly	Me	Ly	Me
0.25	0	0	77.8	69.4	0	0	76.4	55.3
0.5	0	0	100	94.3	0	0	100	79.9
1.0	0	0	100	100	0	0	100	97.6
2.0	0	0	100	100	5.1	0	100	100
3.0	0	0	100	100	21.1	3.9	100	100
4.0	0	0	100	100	43.2	11.8	100	100
5.0	0	0	100	100	59.9	26.3	100	100
Ly=lysine, Me=methionine

[0049] The results of Experiment 1 given in Tables 1 to 3 clearly show that coating agents according to the present invention are disintegrated faster than the comparative coating agents at a pH of 3.0 while providing better inhibition of dissolution at a pH of 6.0.

Experiment 2

[0050] An animal test was carried out in the following manner to investigate the adsorption of the active substance by using 10 sheep (body weight 50-60 kg). Cannulae were inserted into the headgut messenteryic vein, portal fissure vein and carotid artery.

[0051] During the test period, each animal was fed with a basic diet consisting of orchard grass and bran (300 g of each), which was fed twice daily at 7 a.m. and 5 p.m.; 600 g of each meal. Three test feeds were used;

(A) Control feed without a methionine supplement;

(B) Feed containing untreated granules; and

(C) feed containing granules prepared by the method of Example 1 described above. Each feed contained 1.5% (4.5 g) of methionine per 300 g of bran.

[0052] 7 days after the beginning of the test, blood was collected from the carotid artery of each of the test animals to measure the concentration of methionine in the plasma. The results are shown in Table 4.

TABLE 4

Sample	Concentration of methionine (n mol/ml)
	11 a.m.	4 p.m.
A	22.8 ± 1.4	28.3 ± 1.2
B	26.3 ± 0.9	30.3 ± 5.0
C	30.0 ± 1.4	38.5 ± 6.7

[0053] Experiment 2 clearly shows that by addition of a methionine dietary supplement coated with an agent according to the present invention, the concentration of methionine in the plasma increased remarkably in comparison with the results using uncoated granules.

[0054] From these findings, it is apparent that the value of dietary supplements and other active substances may be greatly improved by coating them with an agent according to the present invention.

[0055] Thus by virtue of the coating agent according to the present invention, it is possible to effectively protect supplemental active substances for ruminants from degradation in the first stomach and also to remarkably improve the availability of the active substances in the fourth stomach.

Claims

1. A coating agent for delaying the release of a physiologically active substance to be administered per os to ruminants, comprising a veterinarially acceptable water-soluble, synthetic high molecular compound and ethylcellulose, said coating agent being stable in the first stomach of ruminants and capable of being effectively disintegrated in the fourth stomach of ruminants, characterized in that said coating agent further comprises at least one substance which is miscible with both of said high molecular weight compound and ethylcellulose and is insoluble in water.

2. An agent according to claim 1, in which said synthetic high molecular compound is soluble in water at a pH not exceeding 5.

3. An agent according to claim 1 or claim 2, in which said synthetic high molecular weight compound is selected from;

(a) polyvinyl acetal diethylaminoacetate;

(b) copolymers formed from dimethylaminoethyl meth­acrylate and at least one member selected from alkyl esters of methacrylic acid and alkyl esters of acrylic acid;

(c) copolymers formed from 2-methyl-5-vinylpyridine and at least one member selected from alkyl esters of acrylic acid and alkyl esters of methacrylic acid, methacrylic acid and acrylic acid; and mixtures thereof.

4. An agent according to any one of claims 1 to 3, in which the ratio of said high molecular compound to said ethylcellulose is from 1:0.5 to 1:10 by weight.

5. An agent according to any one of claims 1 to 4, in which said water-soluble substance is solid at room temperature.

6. An agent according to any one of claims 1 to 5, in which said water-insoluble substance comprises one or more of; saturated fatty acids having more than 14 carbon atoms, higher aliphatic alcohols having more than 12 carbon atoms, hardened oils of animal or plant origin, natural resins and synthetic resins, said substance being soluble in organic solvents.

7. An agent according to claim 6, in which said water-insoluble substance is selected from myristic acids, stearic acid, palmitic acid, lauryl alcohol, myristyl alcohol and cetyl alcohol, and stearyl alcohol, hardened oil originating from beef tallow, hardened castor oil, shellac and polyvinyl acetate.

8. An agent according to any one of claims 1 to 7, in which the ratio of said water-soluble substance to said ethylcellulose is from 1:0.1 to 1:20 by weight.

9. An agent according to any one of claims 1 to 8, in which the ratio of said high molecular compound to said water-insoluble substance is more than 50% by weight.

10. A delayed-release veterinary composition for oral administration to ruminants, comprising one or more physiologically active substances coated with an effective amount of a coating agent as claimed in any of claims 1 to 9.

11. A composition according to claim 10, comprising a core of said physiologically active substance provided with a layer fromed by spray-drying said coating agent.

12. A composition according to claim 10, or claim 11, in which the ratio of said coating agent to said core is from 5:100 to 100:100 by weight.

13. Use of a coating agent as claimed in any of claims 1 to 9 for preparing a delayed-release composition for oral administration to ruminants.

14. A process for the preparation of a composition as claimed in any one of claims 10-12, which process comprises drying a granule containing at least one active substance and coating the dried granule with at least one coating agent as claimed in claim 1.

15. A process according to claim 14, in which said granule is produced by adding a binder solution to at least one active substance and kneading the mixture to obtain the desired granule.

16. A process according to claim 14, in which said granule is produced by coating at least one active substance with a binder.

17. A process according to claim 16, in which said granule comprises first and second active substances and is produced by applying a binder onto a core containing at least said first active substance having a higher solubility in water than said second substance, and then applying said second active substance and binder to the core thereby to obtain the desired granule.